Fuel cells are inherently ultra-clean, highly reliable, and have high power density and high energy-conversion efficiency. Also, since fuel cells can operate at an ambient temperature and can be fabricated in miniaturized form and hermetically sealed, they can be extensively applied to power generating systems for home and regional use, medical equipment, military equipment, space equipment, and used as power sources for portable electrical/electronic devices such as mobile telecommunications equipment.
The fuel cell produces electricity through the electrochemical reaction of fuel, such as hydrogen, natural gas, and methanol, and an oxidizing agent. In general, the fuel cell consists of two electrodes—an anode and a cathode, which are sandwhiched around an electrode membrane. The fuel is supplied to the anode where it is electrochemically oxidized, an oxidizing agent, such as oxygen or air, is fed to the cathode where it is electrochemically reduced, and the electrolyte membrane acts as a path for transporting ions produced at the anode to the cathode. Electrons generated at the anode by oxidation of the fuel go through an external circuit, creating a flow of electricity. The protons migrate through the electrolyte to the cathode, where they reunite with the oxidization agent and the electrons to produce water and heat.
A catalyst contained in the anode and the cathode to promote the electrochemical reactions is very important in the fuel cell having such structure. For example, in a polymer electrolyte membrane fuel cell (PEMFC) both of the anode and the cathode generally contain a carbon-supported platinum catalyst having platinum nanoparticles dispersed in a microporous carbon support. Also, in a direct methanol fuel cell the anode catalyst may be, for example, a PtRu alloy powder or a carbon-supported PtRu catalyst having PtRu nanoparticles dispersed in the microporous carbon support, and the cathode catalyst may be, for example, a Pt particle powder or the carbon-supported platinum catalyst having platinum nanoparticles dispersed in the microporous carbon support.
A catalyst support for a fuel cell must exhibit porosity to support and disperse catalytic metal particles and electroconductivity to act as the path for the migration of electrons. In general, amorphous microporous carbon powder known as activated carbon or carbon black may be used as a catalyst support for the fuel cell.
An amorphous microporous carbon powder is generally prepared by chemically and/or physically activating a raw material, such as wood, peat, charcoal, coal, brown coal, coconut peel, and petroleum coke, for example. Generally, the activated carbon has pores exhibiting a diameter of less than about 1 nm and has a surface area of about 60 m2/g to about 1000 m2/g. In particular, Vulcan Black and Kejten Black, which are commercial products most broadly used as a catalyst support, have a surface area of about 230 m2/g and about 800 m2/g, respectively, and have an average primary particle size of less than about 100 nm. Amorphous microporous carbon particles, however, have poor micropore interconnection. Specifically, in a conventional DMFC, a supported catalyst using amorphous microporous carbon particles as a support has lower reactivity than a catalyst consisting of only metal particles. However, DMFCs employing metal particle catalysts are not cost effective due to the high costs associated with the metal particular catalysts. Thus, there is a need to develop a carbon-based catalyst support that is capable of improving the reactivity of the catalyst for fuel cells, such as PEMFCs, PAFCs and DMFC.
For example, the mesoporous carbon molecular sieve, disclosed in Korean Patent Laid-Open Publication No. 2001-0001127 is an example of such a carbon-based catalyst support. This patent discloses a method of preparing an ordered mesoporous carbon molecular sieve using a mesoporous silica molecular sieve, which is prepared using a surfactant as a template material. In this method based on nano-replication, the ordered mesoporous silica molecular sieve, such as “MCM-48” and “SBA-1”, which has micropores connected three-dimensionally by mesopores is used as a template to prepare an ordered mesoporous carbon molecular sieve, such as “CMK-1” and “CMK-2”, which has micropores and mesopores with a uniform diameter and regularly arranged.
The mesoporous carbon molecular sieve prepared as described above may be used as a possible carbon-based catalyst support. However, since the particle size of the mesoporous carbon molecular sieve is larger than those of Vulcan Black and Kejten Black, there is a need to improve the catalytic activity in the mesoporous carbon molecular sieve.